1. Field of the Invention
The present invention relates generally to the forming of sheet metal and, more particularly, to techniques for determining whether sheet metal has been properly formed.
2. Description of the Related Art
Sheet metal is a material that is used in an almost infinite number of ways. It is conventionally used to provide physical support or physical structure in automobiles, furniture, televisions, and other commonly manufactured products. Because there are so many everyday uses for sheet metal, improvements to sheet metal fabrication may be felt by a wide variety of industries.
Sheet metal is also utilized in the electronic industry to provide physical support for electronic devices. In addition, sheet metal may also be used as a housing, a shock absorber or a mounting structure for a component such as a disk drive. Sheet metal is also used for other miscellaneous functions, such as for encasing a power supply or to direct air flow to provide ventilation to a target semiconductor device such as the central processing unit (CPU) or the motherboard of a computer.
As the demand for smaller electronic based devices and machines increase, manufacturers and designers struggle to build components with smaller dimensions that function in a smaller space. Therefore, the precision in which sheet metal parts are fabricated is becoming an increasingly important factor in the overall integrity of the finished package. In current designs, sheet metal must be fabricated within a low tolerance of error because of both the shrinking sizes of electronic components and tighter space limitations and constraints.
To precisely design a sheet metal part, manufacturers typically use computer aided design (CAD) and computer aided manufacturing (CAM) software programs. Not only are CAD/CAM programs able to design the actual structure of the sheet metal part, but the software may also be used to compute the dimensions of a flattened piece of sheet metal from which the sheet metal part is formed and the locations of all the appropriate forming lines to bend the sheet metal. This flattened piece of sheet metal, which is cut to the proper dimensions is called a blank.
A blank may be cut from a large piece of sheet metal by a hard tool stamping or a soft tool having a laser. While the laser offers many conveniences for cutting blanks for specialized sheet metal parts, hard tool stamping, similar to a xe2x80x9ccookie cutterxe2x80x9d, are the standard for mass producing a sheet metal blank. The hard tool stamping cuts the blank by using a stamping die. Depending on the requirements of the finished product, the stamping die may be designed to cut a very precise blank with a very low error tolerance.
While blanks may be manufactured very precisely, the process of bending each blank into the finished sheet metal part is much less exact. Sheet metal is generally formed and shaped by a mechanical or hydraulic press brake machine. A press brake typically includes a slot for inserting a blank or any flattened portion of sheet metal. Most press brakes are manually fed by an operator who holds the workpiece between a punch and a die against an appropriate back stop.
The punch and die are male and female xe2x80x9cVxe2x80x9d shaped parts of the press brake, respectively, that shape the sheet metal. The sheet metal is inserted between a punch and a die by the operator. Then, the press brake is operated by mechanically or hydraulically forcing the punch and die together. Because the sheet metal is between the punch and die, it is bent into the same xe2x80x9cVxe2x80x9d shape. The punch and die may also be made into various other shapes such as a xe2x80x9cWxe2x80x9d depending on the particular need.
The back stop is a gauge that determines whether a piece of sheet metal has been properly positioned into the press brake. When a piece of sheet metal is properly positioned into the press brake, it comes into physical contact with the back stop, which then sends a signal indicating so. Because a press brake is manually operated, the sheet metal forming process is vulnerable to human error, even if a back stop is used. Errors are common because sheet metal is often awkward to handle and may at times be fed into the press brake several times at different angles. Therefore, sheet metal is often not properly positioned in to the press brake, in which case the bend or shape made by the punch and die will be incorrect and the sheet metal will be malformed.
Because errors in handling the sheet metal while using a press brake may be small, it is generally difficult to determine whether a piece of sheet metal was properly formed by the press brake. Precision measuring instruments such as calipers, coordinate measuring machines, micrometers, and gauges may be used to determine how precisely the sheet metal was formed into the desired part. The measurement may then be compared to the specifications on the engineering drawing or CAD file to see if the sheet metal has been properly formed.
However, taking each piece of metal and measuring it for accuracy along every forming line is difficult, time consuming, and potentially expensive. Furthermore, it may not be possible to measure each individual piece if the sheet metal pieces are part of an assembly. In view of the foregoing, it is desirable to have a method and apparatus that provides a marking on the forming line of a piece of sheet metal that allows an operator to visually identify whether there have been errors in the forming process.